INTRAVENOUS CORRECTION OF NEONATAL HYPOMAGNESEMIA - EFFECT ON IONIZEDMAGNESIUM

Objectives: Neonatal hypomagnesemia is defined as total magnesium (TMg ) less than or equal to 0.65 mmol/L, (1.6 mg/dl). However, magnesium ( Mg) deficiency and sufficiency overlap at serum values of 0.57 to 0.74 mmol/L (1.4 to 1.8 mg/dl). We hypothesized that (1) some infants with TMg less than or equal to 0.65 mmol/L (1.6 mg/dl) have normal ionized Mg values (normal neonatal range 0.40 to 0.56 mmol/L (0.97 to 1.36 mg /dl)); (2) the dose (6.0 mg of elemental Mg/kg) used to correct hypoma gnesemia does not lead to elevation of ionized Mg; (3) after intraveno us magnesium sulfate infusion, ionized calcium increases in patients w ith low baseline ionized Mg and decreases in patients with normal base line ionized Mg. Study design: We recruited 22 neonates with TMg less than or equal to 1.6 mg/dl. They received intravenous sulfate (6 mg el emental Mg/kg) over a 1-hour period. Serum TMg, ionized Mg, and ionize d Ca were measured before and after magnesium sulfate infusion. An ion -selective electrode was used to allow direct measurement of ionized M g and ionized Ca. Results: Thirteen (59%) of 22 neonates with TMg less than or equal to 0.65 mmol/L (1.6 mg/dl) had normal IMg. In 7 (31%) o f 22 cases ionized Mg increased slightly above 0.56 mmol/L (1.36 mg/dl ); the maximum value was 0.61 mmol/L (1.48 mg/dl). The change in ioniz ed Ca concentrations and the baseline ionized Mg value were inversely correlated (r = -0.79; p < 0.0001). Conclusions: (1) Measurement of io nized Mg should prevent overdiagnosis and treatment of hypomagnesemia. (2) The dose used in this study is safe. (3) Ionized Mg concentration s are inversely correlated to the response of ionized Ca concentration s to an Mg load.